1. Field of the Invention
The present invention relates to an x-ray target assembly. The x-ray target assembly preferably is used with a charged particle accelerator in a radiation therapy machine.
2. Discussion of Related Art
It is known to produce x-rays by bombarding an x-ray target assembly with electrons emitted from a charged particle accelerator. FIGS. 1 and 2 show an embodiment of a known x-ray target assembly used within radiation therapy machines manufactured and sold by Siemens Medical Solutions of Concord, Calif. under the trade names of Mevatron and Primus. The x-ray target assembly 100 includes a stainless steel cylindrical housing 102 that is supported by a pair of tubes 103.
Within the interior of the housing 102, a graphite cylindrical electron absorber 104 is centrally located within the housing 102 and is supported upon an annular bottom piece 106 of the housing 102. The annular bottom piece 106 is attached to bottom side edges of the housing 102 via mechanical fasteners, such as screws, inserted into openings 108 of the piece 106 and openings of the housing 102.
As shown in FIG. 2, an annular recess 110 is formed within the housing 102. On top of the recess 110 a stainless steel top cover 112 of the housing 102 is attached to the top edges of the housing 102 via a braze or a weld joint. The recess 110 is filled with a cooling fluid, such as water, that flows within tube 103a and enters into the recess 110. The water within the recess 110 is removed therefrom by flowing within tube 103b and exiting from the housing 102. Thus, the arms 103a and b allow for cool water to be continually supplied within the recess 110 and so the x-ray target assembly 100 is continually cooled by water.
A gold target 116 is inserted into the central opening 114 and attached to the edges of the opening 114 via a braze or weld joint. The water within the recess 110 cools the underside of the gold target 116 when the target 116 is being bombarded by electrons.
One disadvantage of the above described anode is that fatigue or stress cracks can be formed in the gold target 116 when bombarded by pulsed electron beams over a period of time. Such cracks can lead to water leaks in the x-ray target assembly 100 which renders the x-ray target assembly 100 inoperable. These water leaks can also cause considerable damage to other components in the radiation therapy machine.
Another disadvantage of the x-ray target assembly 100 described above is that there is a possibility that galvanic corrosion of the braze alloy will occur upon contact of the braze alloy with water. Such corrosion can result in water leaks forming in the x-ray target assembly 100. Such corrosion can be accelerated when the x-ray target assembly 100 is in an environment of ionizing radiation.